Isoniazid-induced cell death is precipitated by underlying mitochondrial complex I dysfunction in mouse hepatocytes

Busulfan induces steatosis in HepaRG cells but not in primary human hepatocytes: Possible explanations and implication for the prediction of drug-induced liver injury

BACKGROUND

The antineoplastic drug busulfan can induce different hepatic lesions including cholestasis and sinusoidal obstruction syndrome. However, hepatic steatosis has never been reported in patients.

OBJECTIVES

This study aimed to determine whether busulfan could induce steatosis in primary human hepatocytes (PHH) and differentiated HepaRG cells.

METHODS

Neutral lipids were determined in PHH and HepaRG cells. Mechanistic investigations were performed in HepaRG cells by measuring metabolic fluxes linked to lipid homeostasis, reduced glutathione (GSH) levels, and expression of genes involved in lipid metabolism and endoplasmic reticulum (ER) stress. Analysis of two previous transcriptomic datasets was carried out.

RESULTS

Busulfan induced lipid accumulation in HepaRG cells but not in six different batches of PHH. In HepaRG cells, busulfan impaired VLDL secretion, increased fatty acid uptake, and induced ER stress. Transcriptomic data analysis and decreased GSH levels suggested that busulfan-induced steatosis might be linked to the high expression of glutathione S-transferase (GST) isoenzyme A1, which is responsible for the formation of the hepatotoxic sulfonium cation conjugate. In keeping with this, the GST inhibitor ethacrynic acid and the chemical chaperone tauroursodeoxycholic acid alleviated busulfan-induced lipid accumulation in HepaRG cells supporting the role of the sulfonium cation conjugate and ER stress in steatosis.

CONCLUSION

While the HepaRG cell line is an invaluable tool for pharmacotoxicological studies, it might not be always an appropriate model to predict and mechanistically investigate drug-induced liver injury. Hence, we recommend carrying out toxicological investigations in both HepaRG cells and PHH to avoid drawing wrong conclusions on the potential hepatotoxicity of drugs and other xenobiotics.

Rifampicin-induced ER stress and excessive cytoplasmic vacuolization instigate hepatotoxicity via alternate programmed cell death paraptosis in vitro and in vivo

AIMS

Rifampicin-induced hepatotoxicity is a primary cause of drug-induced liver injury (DILI), posing a significant challenge to its continued clinical application. Moreover, the mechanism underlying rifampicin-induced hepatotoxicity remains unclear.

MAIN METHODS

Human hepatocyte line-17 (HHL-17) cells were treated with an increasing dose of rifampicin for 24 h, and male Wistar rats were given rifampicin [150 mg/kg body weight (bw)] orally for 28 days. Viability assay, protein expression, and cell death assays were analyzed in vitro. Moreover, liver serum markers, body/organ weight, H&E staining, protein expression, etc., were assayed in vivo.

KEY FINDINGS

Rifampicin induced a dose-dependent hepatotoxicity in HHL-17 cells (IC50; 600 μM), and increased the serum levels of liver injury markers, e.g., alanine transaminase (ALT) and aspartate transaminase (AST) in rats. Rifampicin-induced cell death was non-apoptotic and non-necroptotic both in vitro and in vivo. Further, excessive cellular vacuolization and reduced expression of Alix protein confirmed the induction of paraptosis both in vitro and in vivo. In addition, a significant increase in the endoplasmic reticulum (ER) stress markers (e.g., BiP, CHOP, and total polyubiquitinated proteins) was detected, demonstrating the induction of ER stress and altered protein homeostasis. Interestingly, rifampicin-induced hepatotoxicity was associated with the inhibition of autophagy and enhanced reactive oxygen species (ROS) generation in HHL-17 cells. Furthermore, inhibition of protein synthesis by cycloheximide (CHX) suppressed paraptosis by alleviating rifampicin-induced ER stress and ROS generation.

SIGNIFICANCE

Rifampicin-induced hepatotoxicity involves ER stress-driven paraptosis as a novel mechanism of its toxicity that may be targeted to protect liver cells from rifampicin toxicity.

Serum levels of IL-6/IL-10/GLDH may be early recognition markers of anti-tuberculosis drugs (ATB) -induced liver injury

To explore the potential value of serum glutamate dehydrogenase (GLDH) combined with inflammatory cytokines as diagnostic biomarkers for anti-tuberculosis drug -induced liver injury (ATB-DILI). We collected the residual serum from the patients who met the criteria after liver function tests. We have examined these parameters including GLDH which were determined by enzyme-linked immunosorbent assay and cytokines which were determined by cytokine combination detection kit. Multivariate logistics stepwise forward regression was applied to establish regression models. A total of 138 tuberculosis patients were included in the diagnostic markers study of ATB-DILI, including normal liver function group (n = 108) and ATB-DILI group(n = 30). Serum GLDH, IL-6 and IL-10 levels were significantly increased in the ATB-DILI group. Receiver operating characteristic curve (ROC) curve showed that the area under curve (AUC) of serum GLDH, IL-6 and IL-10 for the diagnosis of ATB-DILI were 0.870, 0.714 and 0.811, respectively. In logistic regression modeling, the AUC of GLDH combined with IL-10 as an ATB-DILI marker is 0.912. Serum IL-6、IL-10 and GLDH levels began to rise preceded the increase in ALT by 7 days, with significant differences in IL-6 compared with 7 days. Serum GLDH, IL-6 and IL-10 levels were correlated with the severity of liver injury. In conclusion, we found that GLDH, IL-6 and IL-10 alone as diagnostic markers of ATB-DILI had good diagnostic efficacy. Logistic regression model established by GLDH and IL-10 had better diagnostic efficacy and IL-6 may be an early predictor of liver injury in the setting of ATB poisoning.

Liver Injury Following Isoniazid Preventive Therapy in HIV Patients Attending Halibet National Referral Hospital, Eritrea: A Prospective Cohort Study

INTRODUCTION

A 6-month course of isoniazid, 300 mg daily, was programmatically introduced in Eritrea in 2014 as tuberculosis preventive therapy in people living with human immunodeficiency virus (PLHIV). The rollout of isoniazid preventive therapy (IPT) in PLHIV was successful in the first 2-3 years. After 2016, rumours based on rare but real incidents of liver injuries following use of IPT spread widely across the country and created concerns amongst healthcare professionals and consumers, that ultimately caused dramatic decline in the rollout of the intervention. Decision makers have been demanding better evidence as previously conducted local studies had inherent methodological limitations. This real-world observational study was conducted to evaluate the risk of liver injury associated with IPT among PLHIV attending Halibet national referral hospital, Asmara, Eritrea.

METHODS

A prospective cohort study, that consecutively enrolled PLHIV attending Halibet hospital, was conducted between 1 March and 30 October 2021. Those exposed to anti-retroviral therapy (ART) plus IPT were considered as exposed and those taking only ART were considered as unexposed. Both groups were prospectively followed up for 4-5 months with monthly liver function tests (LFTs). A Cox proportional hazard model was used to explore whether there was increased risk of drug-induced liver injury (DILI) associated with IPT. Probability of survival without DILI was also estimated using Kaplan-Meier curves.

RESULTS

A total of 552 patients, 284 exposed and 268 unexposed, completed the study, with a mean follow-up time of 3.97 (SD 0.675) months for the exposed and 4.06 (SD 0.675) months for the unexposed. Twelve patients developed drug-induced liver injury (DILI), with a median time-to-onset of 35 days (interquartile range: 26.8, 60 days). All cases were from the exposed group and all except two cases were asymptomatic. The incidence rate of DILI in the exposed group was 10.6 cases per 1000 person-months and zero for the unexposed group (p = 0.002).

CONCLUSION

DILI in PLHIV taking IPT was common; therefore, liver function should be closely monitored to safely administer the product. Despite high levels of deranged liver enzymes, the majority had no symptoms of DILI, emphasising the importance of close laboratory monitoring, especially during the first 3 months of treatment.

Mechanisms of isoniazid and rifampicin-induced liver injury and the effects of natural medicinal ingredients: A review

Isoniazid (INH) and rifampicin (RFP) are the first-line medications for tuberculosis treatment, and liver injury is the major adverse effect. Natural medicinal ingredients provide distinct benefits in alleviating patients’ symptoms, lowering the liver injury risk, delaying disease progression, and strengthening the body’s ability to heal. This paper summarises the recent research on the mechanisms of INH and RFP-induced liver injury and the effects of natural medicinal ingredients. It is believed that INH-induced liver injury may be attributed to oxidative stress, mitochondrial dysfunction, drug metabolic enzymes, protoporphyrin IX accumulation, endoplasmic reticulum stress, bile transport imbalance, and immune response. RFP-induced liver injury is mainly related to cholestasis, endoplasmic reticulum stress, and liver lipid accumulation. However, the combined effect of INH and RFP on liver injury risk is still uncertain. RFP can increase INH-induced hepatotoxicity by regulating the expression of drug-metabolizing enzymes and transporters. In contrast, INH can antagonize RFP-induced liver injury by reducing the total bilirubin level in the blood. Sagittaria sagittifolia polysaccharide, quercetin, gallic acid, and other natural medicinal ingredients play protective roles on INH and RFP-induced liver injury by enhancing the body’s antioxidant capacity, regulating metabolism, inhibiting cell apoptosis, and reducing the inflammatory response. There are still many gaps in the literature on INH and RFP-induced liver injury mechanisms and the effects of natural medicinal ingredients. Thus, further research should be carried out from the perspectives of liver injury phenotype, injury markers, in vitro and in vivo liver injury model construction, and liver-gut axis. This paper comprehensively reviewed the literature on mechanisms involved in INH and RFP-induced liver injury and the status of developing new drugs against INH and RFP-induced liver injury. In addition, this review also highlighted the uses and advantages of natural medicinal ingredients in treating drug-induced liver injury.

Isoxanthohumol, a component of Sophora flavescens, promotes the activation of the NLRP3 inflammasome and induces idiosyncratic hepatotoxicity

ETHNOPHARMACOLOGICAL RELEVANCE

Sophora flavescens is a traditional Chinese medicine commonly used in clinical practice, which has the effects of clearing away heat and dampness. Unfortunately, it has been reported that Sophora flavescens and its preparation may cause liver damage to a certain extent, but the exact mechanism is not clear.

AIM OF THE STUDY

To assess the safety and risk of Sophora flavescens and to elucidate the relationship between Idiosyncratic drug-induced liver injury (IDILI) and the NOD-like receptor family protein 3 (NLRP3) inflammasome.

MATERIALS AND METHODS

Western blot, Caspase-Glo® 1 Inflammasome Assay, ELISA kits, Flow cytometry and FLIPRT Tetra system were used to study the effect of isoxanthohumol (IXN) on the activation of NLRP3 inflammasome and its mechanism. Combined with the lipopolysaccharide-mediated susceptibility IDILI model in mice to evaluate the hepatotoxicity of IXN.

RESULTS

IXN facilitates the activation of caspase-1 and secretion of interleukin (IL)-1β triggered by adenosine triphosphate (ATP), nigericin but not those induced by silicon dioxide and poly (I:C). Furthermore, the activation of NLR-family CARD-containing protein 4 (NLRC4) and the absent in melanoma 2 (AIM2) was not affected by IXN. Mechanistically, IXN promotes NLRP3-dependent apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (ASC) oligomerization and the generation of mitochondrial reactive oxygen species (mtROS) triggered by ATP. The in vivo data showed that non-hepatotoxic doses of IXN resulted in increased levels of glutamate-pyruvate transaminase, glutamate-oxaloacetate transaminase, tumor necrosis factor and IL-1β in the serum and showed increased liver inflammation in the susceptible IDILI model mediated by lipopolysaccharide.

CONCLUSIONS

These results show that IXN enhances NLRP3 inflammasome activation by promoting the accumulation of ATP-induced mtROS and ASC oligomerization to cause IDILI, indicating that IXN may be a risk factor for liver injury caused by the clinical use of Sophora flavescens.

Evaluate the bisphenol A-induced redox state in cells, zebrafish and in vivo with a hydrogen peroxide turn-on fluorescent probe

Hydrogen peroxide (H₂O₂) is an important active oxygen species that plays a major role in redox balance and in physiological and pathological processes of various diseases of biological systems. As H₂O₂ is an endogenous active molecule, fluctuations in H₂O₂ content are not only affected by the state of biological system itself but also easily affected by Bisphenol A (BPA, a typical estrogenic environmental pollutant) in the external environment. Here, the near-infrared fluorescent probe Cy-NOH2 (λ_em = 750 nm) as a tool was synthesized to detect fluctuations in H₂O₂ content in cells and organisms induced by BPA. High sensitivity and excellent selectivity were found when the probe Cy-NOH2 was used to monitor endogenous H₂O₂ in vitro. In addition, the expression of H₂O₂ induced by different concentrations of BPA was able to be detected by the probe. Zebrafish and mice models were induced with different concentrations of BPA, and the H₂O₂ content showed significant increasing trends in zebrafish and livers of mice with increasing BPA concentrations. This study reveals that the probe Cy-NOH2 can be used as an effective tool to monitor the redox state in vivo under the influence of BPA, which provides a basis for clarifying the mechanisms of BPA in a variety of physiological and pathological processes.

Histological and histochemical changes in the peripheral organs of the immune system of dogs in cases of isoniazid poisoning

Most publications on isoniazid poisoning in dogs are devoted to clinical diagnostics, treatment, and prevention of the disease. Histological and histochemical changes are not fully described, though they are important in assessing the toxic effects of isoniazid. Isoniazid is used to treat tuberculosis in humans. Dogs are hypersensitive to this drug. The article highlights the results of macroscopic, histological, and histochemical studies of the dogs’ lymph nodes and spleen in cases of isoniazid poisoning. A pathological examination of 19 corpses of dogs of different ages was performed, during which isoniazid poisoning was posthumously diagnosed, based on anamnesis, clinical signs, pathological autopsy, histological, and histochemical examination. Samples of lymph nodes and spleen were fixed in a 10% aqueous neutral formalin solution, Carnoy’s solution, and Bouin’s fixative. Histoсuts were prepared using a sled microtome and stained with hematoxylin and eosin. Staining was also performed according to the techniques suggested by McManus, Brachet, and Perls. The pathomorphological changes in lymph nodes and spleen were characterized by disorganization of vascular walls and connective tissue fibers of the stroma, dilatation of veins, their overflow with hemolyzed blood, and, in cases of the long clinical course, thrombosis of small vessels. Intravascular hemolysis of erythrocytes resulted in an excessive formation of hemosiderin. Histochemically, the spleen and lymph nodes showed a significant increase in the number of hemosiderophages in the spleen’s red and white pulp and the lymph nodes’ central sinuses and pulp cords. In the spleen, mucoid swelling and necrobiotic changes in the wall structures of the arterioles and arteries progressed with a narrowing of their lumen in dogs suffering from the long clinical course. Increased permeability of the microcirculatory tract vessels of the spleen and lymph nodes, transudate formation, and the destructive changes in the reticular skeleton accompanied hemodynamic violations. A sharp change in blood rheology caused the violation of trophism and metabolism in the immune system. Lymphoid elements of the lymph nodes and white pulp of the spleen were in a state of karyorrhexis and karyolysis. The morphological study of the immune system’s peripheral organs suggests that dogs poisoned by isoniazid demonstrate hemodynamic disorders, changes in the physicochemical properties of blood (hemolysis of erythrocytes and thrombosis). This is the basis of trophic disorders, metabolic malfunctions, and the development of dystrophic processes in all structural elements of the spleen and lymph nodes.

Mechanistic insights into antiretroviral drug-induced liver injury

All classes of antiretroviral therapy (ART) have been implicated to induce adverse drug reactions such drug-induced liver injury (DILI) and immune-mediated adverse reactions in Human Immunodeficiency Virus (HIV) infected individuals. Patients that develop adverse drug reactions tend to have prolonged stays in hospital and may require to change to alternative regimens if reactions persist upon rechallenge or if rechallenge is contraindicated due to severity of the adverse reaction. Diagnosis of DILI remains a huge obstacle that delays timely interventions, since it is still based largely on exclusion of other causes. There is an urgent need to develop robust diagnostic and predictive biomarkers that could be used alongside the available tools (biopsy, imaging, and serological tests for liver enzymes) to give a specific diagnosis of DILI. Crucial to this is also achieving consensus in the definition of DILI so that robust studies can be undertaken. Importantly, it is crucial that we gain deeper insights into the mechanism of DILI so that patients can receive appropriate management. In general, it has been demonstrated that the mechanism of ART-induced liver injury is driven by four main mechanisms: mitochondrial toxicity, metabolic host-mediated injury, immune reconstitution, and hypersensitivity reactions. The focus of this review is to discuss the type and phenotypes of DILI that are caused by the first line ART regimens. Furthermore, we will summarize recent studies that have elucidated the cellular and molecular mechanisms of DILI both in vivo and in vitro.

Drug-induced hepatic steatosis in absence of severe mitochondrial dysfunction in HepaRG cells: proof of multiple mechanism-based toxicity

Steatosis is a liver lesion reported with numerous pharmaceuticals. Prior studies showed that severe impairment of mitochondrial fatty acid oxidation (mtFAO) constantly leads to lipid accretion in liver. However, much less is known about the mechanism(s) of drug-induced steatosis in the absence of severe mitochondrial dysfunction, although previous studies suggested the involvement of mild-to-moderate inhibition of mtFAO, increased de novo lipogenesis (DNL), and impairment of very low-density lipoprotein (VLDL) secretion. The objective of our study, mainly carried out in human hepatoma HepaRG cells, was to investigate these 3 mechanisms with 12 drugs able to induce steatosis in human: amiodarone (AMIO, used as positive control), allopurinol (ALLO), D-penicillamine (DPEN), 5-fluorouracil (5FU), indinavir (INDI), indomethacin (INDO), methimazole (METHI), methotrexate (METHO), nifedipine (NIF), rifampicin (RIF), sulindac (SUL), and troglitazone (TRO). Hepatic cells were exposed to drugs for 4 days with concentrations decreasing ATP level by less than 30% as compared to control and not exceeding 100 × Cmax. Among the 12 drugs, AMIO, ALLO, 5FU, INDI, INDO, METHO, RIF, SUL, and TRO induced steatosis in HepaRG cells. AMIO, INDO, and RIF decreased mtFAO. AMIO, INDO, and SUL enhanced DNL. ALLO, 5FU, INDI, INDO, SUL, RIF, and TRO impaired VLDL secretion. These seven drugs reduced the mRNA level of genes playing a major role in VLDL assembly and also induced endoplasmic reticulum (ER) stress. Thus, in the absence of severe mitochondrial dysfunction, drug-induced steatosis can be triggered by different mechanisms, although impairment of VLDL secretion seems more frequently involved, possibly as a consequence of ER stress.

Idiosyncratic Drug-Induced Liver Injury: Mechanistic and Clinical Challenges

Idiosyncratic drug-induced liver injury (IDILI) remains a significant problem for patients and drug development. The idiosyncratic nature of IDILI makes mechanistic studies difficult, and little is known of its pathogenesis for certain. Circumstantial evidence suggests that most, but not all, IDILI is caused by reactive metabolites of drugs that are bioactivated by cytochromes P450 and other enzymes in the liver. Additionally, there is overwhelming evidence that most IDILI is mediated by the adaptive immune system; one example being the association of IDILI caused by specific drugs with specific human leukocyte antigen (HLA) haplotypes, and this may in part explain the idiosyncratic nature of these reactions. The T cell receptor repertoire likely also contributes to the idiosyncratic nature. Although most of the liver injury is likely mediated by the adaptive immune system, specifically cytotoxic CD8+ T cells, adaptive immune activation first requires an innate immune response to activate antigen presenting cells and produce cytokines required for T cell proliferation. This innate response is likely caused by either a reactive metabolite or some form of cell stress that is clinically silent but not idiosyncratic. If this is true it would make it possible to study the early steps in the immune response that in some patients can lead to IDILI. Other hypotheses have been proposed, such as mitochondrial injury, inhibition of the bile salt export pump, unfolded protein response, and oxidative stress although, in most cases, it is likely that they are also involved in the initiation of an immune response rather than representing a completely separate mechanism. Using the clinical manifestations of liver injury from a number of examples of IDILI-associated drugs, this review aims to summarize and illustrate these mechanistic hypotheses.

Oxidative Stress in Drug-Induced Liver Injury (DILI): From Mechanisms to Biomarkers for Use in Clinical Practice

Idiosyncratic drug-induced liver injury (DILI) is a type of hepatic injury caused by an uncommon drug adverse reaction that can develop to conditions spanning from asymptomatic liver laboratory abnormalities to acute liver failure (ALF) and death. The cellular and molecular mechanisms involved in DILI are poorly understood. Hepatocyte damage can be caused by the metabolic activation of chemically active intermediate metabolites that covalently bind to macromolecules (e.g., proteins, DNA), forming protein adducts-neoantigens-that lead to the generation of oxidative stress, mitochondrial dysfunction, and endoplasmic reticulum (ER) stress, which can eventually lead to cell death. In parallel, damage-associated molecular patterns (DAMPs) stimulate the immune response, whereby inflammasomes play a pivotal role, and neoantigen presentation on specific human leukocyte antigen (HLA) molecules trigger the adaptive immune response. A wide array of antioxidant mechanisms exists to counterbalance the effect of oxidants, including glutathione (GSH), superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPX), which are pivotal in detoxification. These get compromised during DILI, triggering an imbalance between oxidants and antioxidants defense systems, generating oxidative stress. As a result of exacerbated oxidative stress, several danger signals, including mitochondrial damage, cell death, and inflammatory markers, and microRNAs (miRNAs) related to extracellular vesicles (EVs) have already been reported as mechanistic biomarkers. Here, the status quo and the future directions in DILI are thoroughly discussed, with a special focus on the role of oxidative stress and the development of new biomarkers.

Mitochondrial DNA Variants in Patients with Liver Injury Due to Anti-Tuberculosis Drugs

BACKGROUND

Hepatotoxicity is the most severe adverse effect of anti-tuberculosis therapy. Isoniazid's metabolite hydrazine is a mitochondrial complex II inhibitor. We hypothesized that mitochondrial DNA variants are risk factors for drug-induced liver injury (DILI) due to isoniazid, rifampicin or pyrazinamide.

METHODS

We obtained peripheral blood from tuberculosis (TB) patients before anti-TB therapy. A total of 38 patients developed DILI due to anti-TB drugs. We selected 38 patients with TB but without DILI as controls. Next-generation sequencing detected point mutations in the mitochondrial DNA genome. DILI was defined as ALT ≥5 times the upper limit of normal (ULN), or ALT ≥3 times the ULN with total bilirubin ≥2 times the ULN.

RESULTS

In 38 patients with DILI, the causative drug was isoniazid in eight, rifampicin in 14 and pyrazinamide in 16. Patients with isoniazid-induced liver injury had more variants in complex I's NADH subunit 5 and 1 genes, more nonsynonymous mutations in NADH subunit 5, and a higher ratio of nonsynonymous to total substitutions. Patients with rifampicin- or pyrazinamide-induced liver injury had no association with mitochondrial DNA variants.

CONCLUSIONS

Variants in complex I's subunit 1 and 5 genes might affect respiratory chain function and predispose isoniazid-induced liver injury when exposed to hydrazine, a metabolite of isoniazid and a complex II inhibitor.

Mechanistic Studies of Idiosyncratic DILI: Clinical Implications

The idiosyncratic nature of idiosyncratic drug-induced liver injury (IDILI) makes mechanistic studies very difficult, and little is known with certainty. However, the fact that the IDILI caused by some drugs is associated with specific HLA genotypes provides strong evidence that it is mediated by the adaptive immune system. This is also consistent with the histology and the general characteristics of IDILI. However, there are other mechanistic hypotheses. Various in vitro and in vivo systems have been used to test hypotheses. Two other hypotheses are mitochondrial injury and inhibition of the bile salt export pump. It is possible that these mechanisms are responsible for some cases of IDILI or that these mechanisms are complementary and are involved in initiating an immune response. In general, it is believed that the initiation of an immune response requires activation of antigen-presenting cells by molecules such as danger-associated molecular pattern molecules (DAMPs). An attractive hypothesis for the mechanism by which DAMPs induce an immune response is through the activation of inflammasomes. The dominant immune response in the liver is immune tolerance, and it is only when immune tolerance fails that significant liver injury occurs. Consistent with this concept, an animal model was developed in which immune checkpoint inhibition unmasked the ability of drugs to cause liver injury. Although it appears that the liver damage is mediated by the adaptive immune system, an innate immune response is required for an adaptive immune response. The innate immune response is not dependent on specific HLA genes or T cell receptors and may occur in most patients and animals treated with a drug that can cause IDILI. Studies of the subclinical innate immune response to drugs may provide important mechanistic clues and provide a method to screen drugs for their potential to cause IDILI.

Rotenone Increases Isoniazid Toxicity but Does Not Cause Significant Liver Injury: Implications for the Hypothesis that Inhibition of the Mitochondrial Electron Transport Chain Is a Common Mechanism of Idiosyncratic Drug-Induced Liver Injury

Idiosyncratic drug reactions (IDRs) significantly increase the risk of failure in drug development. The major IDR leading to drug candidate failure is idiosyncratic drug-induced liver injury (IDILI). Although most evidence suggests that IDRs are mediated by the immune system, there are other hypotheses, such as mitochondrial dysfunction. Many pharmaceutical companies routinely screen for mitochondrial toxicity in an attempt to "derisk" drug candidates. However, the basic hypothesis has never been rigorously tested. A major assay used for this screening involves measurement of inhibition of the mitochondrial electron transport chain. One study found that the combination of rotenone and isoniazid, which inhibit mitochondrial complex I and II, respectively, were synergistic in causing hepatocyte toxicity in vitro and suggested the combination of another drug that inhibited complex I would increase the risk of isoniazid-induced liver injury in patients. We tested this hypothesis in vivo where wild-type and PD-1-/- mice administered anti-CTLA-4, our impaired immune tolerance mouse model, were given 0.02% (w/v) rotenone in water or 0.1%, 0.05%, and 0.01% (w/w) rotenone alone or in combination with isoniazid in food. The cotreatment led to lethality in 100% of the animals receiving 0.1% rotenone and 0.2% isoniazid and 83% of the animals cotreated with 0.05% rotenone and 0.2% isoniazid in food. Nevertheless, there was no significant increase in GLDH or histological evidence of liver injury. No signs of toxicity were observed in any of the mice given rotenone or isoniazid alone. Even though inhibition of the mitochondrial electron transport chain did not lead to significant liver toxicity, it could provide danger signals that promote immune-mediated liver injury. However, rotenone did not significantly increase the liver injury induced by isoniazid in our impaired immune tolerance model. Overall, we conclude that inhibition of the mitochondrial electron transport chain is not a significant mechanism of IDILI.

Prominence of Oxidative Stress in the Management of Anti-tuberculosis Drugs Related Hepatotoxicity

Advanced medical services and treatments are available for treating Tuberculosis. Related prevalence has increased in recent times. Unfortunately, the continuous consumption of related drugs is also known for inducing hepatotoxicity which is a critical condition and cannot be overlooked. The present review article has focused on the pathways causing these toxicities and also the role of enzyme CYP2E1, hepatic glutathione, Nrf2-ARE signaling pathway, and Membrane Permeability Transition as possible targets which may help in preventing the hepatotoxicity induced by the drugs used in the treatment of tuberculosis.

A near-infrared fluorescent probe for evaluating endogenous hydrogen peroxide during ischemia/reperfusion injury

A fluorescent probe, Cy-ArB, is developed for real-time monitoring of H₂O₂ fluctuations in cells and in vivo during ischemia/reperfusion processes.

Rhabdomyolysis Induced by Isoniazid in a Patient with Rheumatoid Arthritis and End-stage Renal Disease: A Case Report and Review of the Literature

A 76-year-old man complicated with end-stage renal disease had latent tuberculosis infection (LTBI), and isoniazid (INH) 300 mg daily was started to prevent reactivation of LTBI before using biologic agents for rheumatoid arthritis. On the 8th day after administration of INH, he presented with a fever, petechiae, and myalgia. Serological studies revealed elevated myogenic enzymes and creatinine level. Based on the exclusion of other etiologies, rapid improvement with cessation of INH, and the recurrence of the fever and myalgia with re-administration of a reduced dose of INH, we diagnosed him with INH-induced rhabdomyolysis. Physicians should be aware of rhabdomyolysis induced by INH at a therapeutic dose as an infrequent but potentially fatal adverse drug reaction.

Biomarkers of drug-induced liver injury: progress and utility in research, medicine, and regulation

INTRODUCTION

The difficulty of understanding and diagnosing drug-induced liver injury (DILI) has led to proliferation of serum and genetic biomarkers. Many applications of these biomarkers have been proposed, including investigation of mechanisms, prediction of DILI during early trials or before initiation of therapy in patients, and diagnosis of DILI during therapy. Areas covered: We review the definition and categories of DILI, describe recent developments in DILI biomarker development, and provide guidance for future directions in DILI biomarker research. Expert commentary: There are major obstacles to DILI biomarker development and implementation, including the low prevalence of idiosyncratic DILI (IDILI), weak associations of IDILI with genetic variants, and lack of specificity of many biomarkers for the liver. Certain serum biomarkers, like miR-122, may have clinical utility in early-presenting patients with either intrinsic or idiosyncratic DILI in the future, while others likely will not find use. Future research should focus on implementation of biomarkers to predict later injury and outcome in early presenters with intrinsic DILI, and on development of biomarkers of adaptation and repair in the liver that can be used to determine if a liver test abnormality is likely to be clinically significant in IDILI.

Do In Vitro Assays Predict Drug Candidate Idiosyncratic Drug-Induced Liver Injury Risk?

In vitro assays are commonly used during drug discovery to try to decrease the risk of idiosyncratic drug-induced liver injury (iDILI). But how effective are they at predicting risk? One of the most widely used methods evaluates cell cytotoxicity. Cytotoxicity assays that used cell lines that are very different from normal hepatocytes, and high concentrations of drug, were not very accurate at predicting idiosyncratic drug reaction risk. Even cytotoxicity assays that use more biologically normal cells resulted in many false-positive and false-negative results. Assays that quantify reactive metabolite formation, mitochondrial injury, and bile salt export pump (BSEP) inhibition have also been described. Although evidence suggests that reactive metabolite formation and BSEP inhibition can play a role in the mechanism of iDILI, these assays are not very accurate at predicting risk. In contrast, inhibition of the mitochondrial electron transport chain appears not to play an important role in the mechanism of iDILI, although other types of mitochondrial injury may do so. It is likely that there are many additional mechanisms by which drugs can cause iDILI. However, simply measuring more parameters is unlikely to provide better predictive assays unless those parameters are actually involved in the mechanism of iDILI. Hence, a better mechanistic understanding of iDILI is required; however, mechanistic studies of iDILI are very difficult. There is substantive evidence that most iDILI is immune mediated; therefore, the most accurate assays may involve those that determine immune responses to drugs. New methods to manipulate immune tolerance may greatly facilitate development of more suitable methods.

Mitochondrial dysfunction as a mechanism of drug-induced hepatotoxicity: current understanding and future perspectives

Mitochondria are critical cellular organelles for energy generation and are now also recognized as playing important roles in cellular signaling. Their central role in energy metabolism, as well as their high abundance in hepatocytes, make them important targets for drug-induced hepatotoxicity. This review summarizes the current mechanistic understanding of the role of mitochondria in drug-induced hepatotoxicity caused by acetaminophen, diclofenac, anti-tuberculosis drugs such as rifampin and isoniazid, anti-epileptic drugs such as valproic acid and constituents of herbal supplements such as pyrrolizidine alkaloids. The utilization of circulating mitochondrial-specific biomarkers in understanding mechanisms of toxicity in humans will also be examined. In summary, it is well-established that mitochondria are central to acetaminophen-induced cell death. However, the most promising areas for clinically useful therapeutic interventions after acetaminophen toxicity may involve the promotion of adaptive responses and repair processes including mitophagy and mitochondrial biogenesis, In contrast, the limited understanding of the role of mitochondria in various aspects of hepatotoxicity by most other drugs and herbs requires more detailed mechanistic investigations in both animals and humans. Development of clinically relevant animal models and more translational studies using mechanistic biomarkers are critical for progress in this area.

Relevance for patients:This review focuses on the role of mitochondrial dysfunction in liver injury mechanisms of clinically important drugs like acetaminophen, diclofenac, rifampicin, isoniazid, amiodarone and others. A better understanding ofthe mechanisms in animal models and their translation to patients will be critical for the identification of new therapeutic targets.

Deficiency of N-acetyltransferase increases the interactions of isoniazid with endobiotics in mouse liver

Acetylation is the major metabolic pathway of isoniazid (INH) mediated by N-acetyltransferases (NATs). Previous reports suggest that slow acetylators have higher risks of INH hepatotoxicity than rapid acetylators, but the detailed mechanisms remain elusive. The current study used Nat1/2(-/-) mice to mimic NAT slow metabolizers and to investigate INH metabolism in the liver. We found that INH acetylation is abolished in the liver of Nat1/2(-/-) mice, suggesting that INH acetylation is fully dependent on NAT1/2. In addition to the acetylation pathway, INH can be hydrolyzed to form hydrazine (Hz) and isonicotinic acid (INA). We found that INA level was not altered in the liver of Nat1/2(-/-) mice, indicating that deficiency of NAT1/2 has no effect on INH hydrolysis. Because INH acetylation was abolished and INH hydrolysis was not altered in Nat1/2(-/-) mice, we expected an extremely high level of INH in the liver. However, we only observed a modest accumulation of INH in the liver of Nat1/2(-/-) mice, suggesting that there are alternative pathways in INH metabolism in NAT1/2 deficient condition. Our further studies revealed that the conjugated metabolites of INH with endobiotics, including fatty acids and vitamin B6, were significantly increased in the liver of Nat1/2(-/-) mice. In summary, this study illustrated that deficiency of NAT1/2 decreases INH acetylation, but increases the interactions of INH with endobiotics in the liver. These findings can be used to guide future studies on the mechanisms of INH hepatotoxicity in NAT slow metabolizers.

A mitochondrial-targeting near-infrared fluorescent probe for bioimaging and evaluating endogenous superoxide anion changes during ischemia/reperfusion injury

The outburst of superoxide anion (O₂^-) in mitochondrial during ischemia/reperfusion (I/R) process will cause a series of oxidative damage including polarity loss of mitochondrial membrane potential, overload of secondary cellular calcium, and cascade apoptosis. To monitor the O₂^- level fluctuations as well as to evaluate the relationship between O₂^- concentration and the degree of cell apoptosis during I/R process, we propose a ratiometric near-infrared mitochondrial targeting fluorescent probe Mito-Cy-Tfs for the detection of level changes of O₂^- in cells and in vivo. The probe Mito-Cy-Tfs is composed of three moieties: near-infrared heptamethine cyanine as fluorescence signal transducer, trifluoromethanesulfonamide as fluorescence modulator, and lipophilic triphenylphosphonium cation as mitochondrial guider. The probe can well locate in mitochondria and respond the concentration changes of endogenous O₂^- selectively and sensitively. The probe has been successfully utilized to image the endogenous O₂^- fluctuations in four kinds of cell I/R models (glucose deprivation/reperfusion, serum deprivation/reperfusion, oxygen deprivation/reperfusion and glucose-serum-oxygen deprivation/reperfusion). The probe also exhibits deep tissue penetration for real-time imaging of O₂^-concentration in liver of I/R mice model. We confirm that the adoption of ischemic preconditioning (IPC) and postconditioning (IPTC) can protect liver from I/R injury. The probe can be employed to accurately indicate and evaluate the mutual relationship between the levels of O₂^- and the degrees of organ damage during I/R, IPC and IPTC processes. The above applications make our new probe a potential candidate for the clinical surgery assessment.

Impairment of Mitochondrial Biogenesis and Dynamics Involved in Isoniazid-Induced Apoptosis of HepG2 Cells Was Alleviated by p38 MAPK Pathway

Isoniazid (INH), a widely used first-line antitubercular drug, has been noted to be associated with hepatotoxicity. In spite of extensive researches over many decades, the mechanism of INH-induced hepatotoxicity still remains poorly understood. Recently, mitochondrial toxicity has been emerging as a new paradigm for INH-induced hepatotoxicity. In this study, we showed that INH impaired mitochondrial biogenesis and dynamics in human hepatocarcinoma HepG2 cells. INH reduced mitochondrial membrane potential (MMP) and induced mitochondria swelling. INH also inhibited the protein expressions of three major mitochondrial biogenesis regulators, SIRT1, PGC1α and NRF1, along with increased acetylation of PGC1α. Meanwhile, INH decreased the number of mitochondria, accompanied by decreased expression of mitochondrial protein COX IV. INH caused mitochondrial fragmentation involving decreased levels of the fusion protein MFN2 as well as the fission protein DRP1. INH-reduced DRP1 expression was associated with the increase of apoptosis, suggesting the existence of pro-survival fission and its involvement in mitochondrial quality control. INH activated p38 MAPK, whereas inhibition of p38 MAPK aggravated INH-induced decreases of SIRT1, PGC1α, NRF1, COX IV and DRP1 expressions. P38 MAPK inhibition also further up-regulated the acetylation of PGC1α and exacerbated INH-induced MMP loss, mitochondrial swelling and apoptosis. Taken together, INH-activated p38 MAPK induced mitochondrial biogenesis to alleviate apoptosis through partly recovering SIRT1-PGC1α pathway activation. In the meantime, p38 MAPK activation by INH promoted protective mitochondrial fission to alleviate apoptosis by partial recovery of DRP1 expression.

Customised in vitro model to detect human metabolism-dependent idiosyncratic drug-induced liver injury

Drug-induced liver injury (DILI) has a considerable impact on human health and is a major challenge in drug safety assessments. DILI is a frequent cause of liver injury and a leading reason for post-approval drug regulatory actions. Considerable variations in the expression levels of both cytochrome P450 (CYP) and conjugating enzymes have been described in humans, which could be responsible for increased susceptibility to DILI in some individuals. We herein explored the feasibility of the combined use of HepG2 cells co-transduced with multiple adenoviruses that encode drug-metabolising enzymes, and a high-content screening assay to evaluate metabolism-dependent drug toxicity and to identify metabolic phenotypes with increased susceptibility to DILI. To this end, HepG2 cells with different expression levels of specific drug-metabolism enzymes (CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4, GSTM1 and UGT2B7) were exposed to nine drugs with reported hepatotoxicity. A panel of pre-lethal mechanistic parameters (mitochondrial superoxide production, mitochondrial membrane potential, ROS production, intracellular calcium concentration, apoptotic nuclei) was used. Significant differences were observed according to the level of expression and/or the combination of several drug-metabolism enzymes in the cells created ad hoc according to the enzymes implicated in drug toxicity. Additionally, the main mechanisms implicated in the toxicity of the compounds were also determined showing also differences between the different types of cells employed. This screening tool allowed to mimic the variability in drug metabolism in the population and showed a highly efficient system for predicting human DILI, identifying the metabolic phenotypes associated with increased DILI risk, and indicating the mechanisms implicated in their toxicity.

Evaluation of HepaRG cells for the assessment of indirect drug-induced hepatotoxicity using INH as a model substance

HepaRG cells are widely used as an in vitro model to assess drug-induced hepatotoxicity. However, only few studies exist so far regarding their suitability to detect the effects of drugs requiring a preceding activation via the cytochrome P450 (CYP) system. A prototypic substance is the anti-tuberculosis agent INH, which is metabolized into N-acetylhydrazine, which then triggers hepatotoxicity. Therefore, the aim of the present study was to test if this effect can also be detected in HepaRG cells and if it can be counteracted by the known hepatoprotectant silibinin. For this purpose, differentiated HepaRG cells were treated with increasing concentrations of INH (0.1-100 mM) or 10 mM INH plus escalating concentrations of silibinin (1-100 µM). After 48 h of treatment, cell morphology and parameters indicating cell vitality, oxidative stress, and liver cell function were assessed. High concentrations of INH led to severe histopathological changes, reduced cell vitality and glutathione content, increased LDH and ASAT release into the medium, enhanced lipid peroxidation, and elevated cleaved caspase-3 expression. Additionally, glycogen depletion and reduced biotransformation capacity were seen at high INH concentrations, whereas at low concentrations an induction of biotransformation enzymes was noticed. Silibinin caused clear-cut protective effects, but with few parameters INH toxicity was even aggravated, most probably due to increased metabolization of INH into its toxic metabolite. In conclusion, HepaRG cells are excellently suited to evaluate the effects of substances requiring prior toxification via the CYP system, such as INH. They additionally enable the identification of complex substance interactions.

Dexamethasone Pretreatment Alleviates Isoniazid/Lipopolysaccharide Hepatotoxicity: Inhibition of Inflammatory and Oxidative Stress

Isoniazid (INH) remains a cornerstone key constitute of the current tuberculosis management strategy, but its hepatotoxic potentiality remains a significant clinical problem. Our previous findings succeed to establish a rat model of INH hepatotoxicity employing the inflammatory stress theory in which non-injurious doses of inflammatory-mediating agent bacterial lipopolysaccharides (LPS) augmented the toxicity of INH that assist to uncover the mechanisms behind INH hepatotoxicity. Following LPS exposure, several inflammatory cells are activated and it is likely that the consequences of this activation rather than direct hepatocellular effects of LPS underlie the ability of LPS to augment toxic responses. In this study, we investigated the potential protective role of the anti-inflammatory agent dexamethasone (DEX), a potent synthetic glucocorticoid, in INH/LPS hepatotoxic rat model. DEX pre-treatment successfully eliminates the components of the inflammatory stress as shown through analysis of blood biochemistry and liver histopathology. DEX potentiated hepatic anti-oxidant mechanisms while serum and hepatic lipid profiles were reduced. However, DEX administration was not able to revoke the principal effects of cytochrome P450 2E1 (CYP2E1) in INH/LPS-induced liver damage. In conclusion, this study illustrated the DEX-preventive capabilities on INH/LPS-induced hepatotoxicity model through DEX-induced potent anti-inflammatory activity whereas the partial toxicity seen in the model could be attributed to the expression of hepatic CYP2E1. These findings potentiate the clinical applications of DEX co-administration with INH therapy in order to reduce the potential incidences of hepatotoxicity.

Toxicological Implications of Mitochondrial Localization of CYP2E1

Cytochrome P450 2E1 (CYP2E1) metabolizes an extensive array of pollutants, drugs, and other small molecules, often resulting in bioactivation to reactive metabolites. Therefore, it is unsurprising that it has been the subject of decades of research publications and reviews. However, while CYP2E1 has historically been studied in the endoplasmic reticulum (erCYP2E1), active CYP2E1 is also present in mitochondria (mtCYP2E1). Relatively few studies have specifically focused on mtCYP2E1, but there is growing interest in this form of the enzyme as a driver in toxicological mechanisms given its activity and location. Many previous studies have linked total CYP2E1 to conditions that involve mitochondrial dysfunction (fasting, diabetes, non-alcoholic steatohepatitis, and obesity). Furthermore, a large number of reactive metabolites that are formed by CYP2E1 through metabolism of drugs and pollutants have been demonstrated to cause mitochondrial dysfunction. Finally, there appears to be significant inter-individual variability in targeting to the mitochondria, which could constitute a source of variability in individual response to exposures. This review discusses those outcomes, the biochemical properties and toxicological consequences of mtCYP2E1, and highlights important knowledge gaps and future directions. Overall, we feel that this exciting area of research is rich with new and important questions about the relationship between mtCYP2E1, mitochondrial dysfunction, and pathology.

Isoniazid metabolism and hepatotoxicity

Isoniazid (INH) is highly effective for the management of tuberculosis. However, it can cause liver injury and even liver failure. INH metabolism has been thought to be associated with INH-induced liver injury. This review summarized the metabolic pathways of INH and discussed their associations with INH-induced liver injury.

Role of Inflammatory and Oxidative Stress, Cytochrome P450 2E1, and Bile Acid Disturbance in Rat Liver Injury Induced by Isoniazid and Lipopolysaccharide Cotreatment

Isoniazid (INH) remains the core drug in tuberculosis management, but serious hepatotoxicity and potentially fatal liver injury continue to accompany INH consumption. Among numerous theories that have been established to explain INH-induced liver injury, an inflammatory stress theory has recently been widely used to explain the idiosyncrasy. Inflammatory stress usually sensitizes tissues to a drug's toxic consequences. Therefore, the present study was conducted to verify whether bacterial lipopolysaccharide (LPS)-induced inflammation may have a role in enhancing INH hepatotoxicity. While single INH or LPS administration showed no major toxicity signs, INH-LPS cotreatment intensified liver toxicity. Both blood biomarkers and histological evaluations clearly showed positive signs of severe liver damage accompanied by massive necrosis, inflammatory infiltration, and hepatic steatosis. Furthermore, elevated serum levels of bile acid associated with the repression of bile acid synthesis and transport regulatory parameters were observed. Moreover, the principal impact of cytochrome P450 2E1 (CYP2E1) on INH toxicity could be anticipated, as its protein expression showed enormous increases in INH-LPS-cotreated animals. Furthermore, the crucial role of CYP2E1 in the production of reactive oxygen species (ROS) was clearly obvious in the repression of hepatic antioxidant parameters. In summary, these results confirmed that this LPS-induced inflammation model might prove valuable in revealing the hepatotoxic mechanisms of INH and the crucial role played by CYP2E1 in the initiation and propagation of INH-induced liver damage, information which could be very useful to clinicians in understanding the pathogenesis of drug-induced liver injury.

A High Dose of Isoniazid Disturbs Endobiotic Homeostasis in Mouse Liver

Overdose of isoniazid (INH), an antituberculosis drug, can be life-threatening because of neurotoxicity. In clinical practice for management of INH overdose and acute toxicity, the potential of INH-induced hepatotoxicity is also considered. However, the biochemical basis of acute INH toxicity in the liver remains elusive. In the current study, we used an untargeted metabolomic approach to explore the acute effects of INH on endobiotic homeostasis in mouse liver. We found that overdose of INH resulted in accumulation of oleoyl-l-carnitine and linoleoyl-l-carnitine in the liver, indicating mitochondrial dysfunction. We also revealed the interactions between INH and fatty acyl-CoAs by identifying INH-fatty acid amides. In addition, we found that overdose of INH led to the accumulation of heme and oxidized NAD in the liver. We also identified an INH and NAD adduct in the liver. In this adduct, the nicotinamide moiety in NAD was replaced by INH. Furthermore, we illustrated that overdose of INH depleted vitamin B6 in the liver and blocked vitamin B6-dependent cystathionine degradation. These data suggest that INH interacts with multiple biochemical pathways in the liver during acute poisoning caused by INH overdose.

The hydroxypyridinone iron chelator CP94 increases methyl-aminolevulinate-based photodynamic cell killing by increasing the generation of reactive oxygen species

Methyl-aminolevulinate-based photodynamic therapy (MAL-PDT) is utilised clinically for the treatment of non-melanoma skin cancers and pre-cancers and the hydroxypyridinone iron chelator, CP94, has successfully been demonstrated to increase MAL-PDT efficacy in an initial clinical pilot study. However, the biochemical and photochemical processes leading to CP94-enhanced photodynamic cell death, beyond the well-documented increases in accumulation of the photosensitiser protoporphyrin IX (PpIX), have not yet been fully elucidated. This investigation demonstrated that MAL-based photodynamic cell killing of cultured human squamous carcinoma cells (A431) occurred in a predominantly necrotic manner following the generation of singlet oxygen and ROS. Augmenting MAL-based photodynamic cell killing with CP94 co-treatment resulted in increased PpIX accumulation, MitoSOX-detectable ROS generation (probably of mitochondrial origin) and necrotic cell death, but did not affect singlet oxygen generation. We also report (to our knowledge, for the first time) the detection of intracellular PpIX-generated singlet oxygen in whole cells via electron paramagnetic resonance spectroscopy in conjunction with a spin trap.

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Augmentation of MAL-based photodynamic cell killing with CP94 increases necrosis.

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CP94 augmentation increases generation of ROS, likely to be mitochondria-localised.

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PpIX-generated ¹O₂ was detected in whole cells by EPR spectroscopy.

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Photodynamic cell killing was dependent primarily on ¹O₂.

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Superoxide/other ROS also contributed to the efficacy of photodynamic cell killing.

The unique chemistry and biology of the piericidins

The piericidin family of microbial metabolites features a 4-pyridinol core linked with a methylated polyketide side chain. Piericidins are exclusively produced by actinomycetes, especially members of the genus Streptomyces. The close structural similarity with coenzyme Q renders the piericidins important NADH-ubiquinone oxidoreductase (complex I) inhibitors in the mitochondrial electron transport chain. Because of the significant activities of the piericidins, which include insecticidal, antimicrobial and antitumor effects, total syntheses of the piericidins were developed using various synthetic strategies. The biosynthetic origin of this class has also been the subject of investigation. This review covers the isolation and structure determination of the natural piericidins, their chemical modification, the total syntheses of natural and unnatural analogs, their biosynthesis, and reported biological activities together with structure-activity relationships. Given the fundamental biology of this class of metabolites, the piericidin family will likely continue to attract attention as biological probes of important biosynthetic processes.

Induction of protective autophagy against apoptosis in HepG2 cells by isoniazid independent of the p38 signaling pathway

Isoniazid (INH), one of the first-line anti-tuberculosis drugs, is adversely associated with hepatotoxicity in the clinic. However, the detailed mechanism of this side effect is still unclear. The traditional theory that cytochrome P450 2E1 is involved in INH-induced hepatotoxicity remains controversial, therefore other mechanisms by which INH exerts hepatotoxicity need to be investigated. In the current study, we showed that in vitro treatment of human hepatocarcinoma HepG2 cells with INH induced caspase-dependent apoptosis through extrinsic and intrinsic pathways. It was characterized by the increased population of apoptotic cells using Annexin V/propidium iodide (PI) double staining by flow cytometry, and by the activation of caspases 8, 9, 3 and poly (ADP-ribose)-polymerase (PARP) proteins by western blotting. INH treatment also induced autophagy as shown by the upregulated levels of microtubule-associated protein 1 light chain 3-II (LC3-II), increased GFP-LC3 punctates, and elevated monodansylcadaverine (MDC) fluorescence intensity. The measurement of the autophagic flux using chloroquine (CQ) confirmed that INH stimulated autophagy but did not inhibit it by impairing lysosomal degradation. The blockage of autophagy with CQ exacerbated INH-induced apoptosis significantly. Further study showed that INH treatment down-regulated the protein phosphorylation of the mammalian target of rapamycin (mTOR), the key negative regulator of autophagy. In addition, INH induced p38 signaling activation. SB203580, a p38 inhibitor, effectively enhanced INH-induced apoptosis by increasing the cleavages of caspases 9, 3 and PARP, but did not affect autophagy. In summary, we firstly found that INH induced a protective autophagy which was associated with the inhibition of the mTOR pathway, and that INH induced p38 signaling activation to inhibit apoptosis by down-regulation of caspases 9, 3 and PARP pathways, but not that of autophagy. Thus, activation of autophagy and p38 signaling is presumably a therapeutic strategy for INH-induced hepatotoxicity.

Mycobacterial Interspersed Repetitive Unit Can Predict Drug Resistance of Mycobacterium tuberculosis in China

Background: Recently, Mycobacterial Interspersed Repetitive Unit (MIRU) was supposed to be associated with drug resistance in Mycobacterium tuberculosis (M. tuberculosis), but whether the association exists actually in local strains in China was still unknown. This research was conducted to explore that association and the predictability of MIRU to drug resistance of Tuberculosis (TB).

Methods: The clinical isolates were collected and the susceptibility test were conducted with Lowenstein–Jensen (LJ) medium for five anti-TB drug. Based on PCR of MIRU-VNTR (Variable Number of Tandem Repeat) genotyping, we tested the number of the repeat unite of MIRU. Then, we used logistic regression to evaluate the association between 15 MIRU and drug resistance. In addition, we explored the most suitable MIRU locus of identified MIRU loci for drug resistance by multivariate logistic regression.

Results: Of the 102 strains, one isolate was resistant to rifampicin and one isolate was resistant to streptomycin. Among these fifteen MIRU, there was a association between MIRU loci polymorphism and anti-tuberculosis drug resistance, ETRB (P = 0.03, OR = 0.19, 95% CI 0.05–0.81) and ETRC (P = 0.01, OR = 0.14, 95% CI 0.03–0.64) were negatively related to isoniazid resistance; MIRU20 (P = 0.05, OR = 2.87, 95% CI 1.01–8.12) was positively associated with ethambutol resistance; and QUB11a (P = 0.02, OR = 0.79, 95% CI 0.65–0.96) was a negative association factor of p-aminosalicylic acid resistance.

Conclusion: Our research showed that MIRU loci may predict drug resistance of tuberculosis in China. However, the mechanism still needs further exploration.

Targeting mitochondrial function to protect against vision loss

INTRODUCTION

Mitochondria, essential to multicellular life, convert food into ATP to satisfy cellular energy demands. Since different tissues have different energy requirements, mitochondrial density is high in tissues with high metabolic needs, such as the visual system, which is therefore highly susceptible to limited energy supply as a result of mitochondrial dysfunction.

AREAS COVERED

Vision impairment is a common feature of most mitochondrial diseases. At the same time, there is mounting evidence that mitochondrial impairment contributes to the pathogenesis of major eye diseases such as glaucoma and might also be involved in the reported vision impairment in neurodegenerative disorders such as Alzheimer's disease.

EXPERT OPINION

Rather than relying on symptomatic treatment, acknowledging the mitochondrial origin of visual disorders in mitochondrial, neurodegenerative and ocular diseases could lead to novel therapeutics that aim to modulate mitochondrial function in order to protect against vision loss. This approach has already shown some promising clinical results in inherited retinal disorders, which supports the idea that targeting mitochondria could also be a treatment option for other optic neuropathies.

Deoxidation rates play a critical role in DNA damage mediated by important synthetic drugs, quinoxaline 1,4-dioxides

Quinoxaline 1,4-dioxides (QdNOs) are synthetic agents with a wide range of biological activities. However, the mechanism of DNA damage mediated by QdNOs is far from clear. Five classical QdNOs, quinocetone (QCT), mequindox (MEQ), carbadox (CBX), olaquindox (OLA), and cyadox (CYA), were used to investigate the genotoxicity of QdNOs. The deoxidation rate of QdNOs was presumed to play a role in their genotoxicity. Deoxidation rates of QdNOs in both rat and pig liver microsomes were investigated using LC/MS-IT/TOF, and their relative quantification was achieved with HPLC. To reveal the relationships between the deoxidation rate and genotoxicity, cell damage, oxidative stress, and DNA damage were detected. Under low oxygen conditions, the rank order of the desoxy and bidesoxy rates in rat and pig liver microsomes was QCT < CBX < MEQ < OLA < CYA and QCT < MEQ < CBX < OLA < CYA, respectively. Only desoxy-quinoxalines were detected under aerobic conditions. The concentrations of deoxidized metabolites under low oxygen conditions were at least 6 times higher than those under aerobic conditions. In rats, porcine primary hepatocytes, and HepG2 cells, oxidative stress indices and DNA damage showed inverse relationships with the deoxidation rate, indicating that the deoxidation rate of QdNOs, especially bidesoxy rates, might play a critical role in mediating their ability to promote DNA damage. These results indicated that faster deoxidation of QdNOs results in lower DNA-damage-induced toxicity. Our results shed new light on the prevention of DNA damage mediated by QdNOs and help to understand the relationships among the chemical structures, metabolism, and DNA damage of QdNOs.

Mechanisms of cell death pathway activation following drug-induced inhibition of mitochondrial complex I

Respiratory complex I inhibition by drugs and other chemicals has been implicated as a frequent mode of mitochondria-mediated cell injury. However, the exact mechanisms leading to the activation of cell death pathways are incompletely understood. This study was designed to explore the relative contributions to cell injury of three distinct consequences of complex I inhibition, i.e., impairment of ATP biosynthesis, increased formation of superoxide and, hence, peroxynitrite, and inhibition of the mitochondrial protein deacetylase, Sirt3, due to imbalance of the NADH/NAD(+) ratio. We used the antiviral drug efavirenz (EFV) to model drug-induced complex I inhibition. Exposure of cultured mouse hepatocytes to EFV resulted in a rapid onset of cell injury, featuring a no-effect level at 30µM EFV and submaximal effects at 50µM EFV. EFV caused a concentration-dependent decrease in cellular ATP levels. Furthermore, EFV resulted in increased formation of peroxynitrite and oxidation of mitochondrial protein thiols, including cyclophilin D (CypD). This was prevented by the superoxide scavenger, Fe-TCP, or the peroxynitrite decomposition catalyst, Fe-TMPyP. Both ferroporphyrins completely protected from EFV-induced cell injury, suggesting that peroxynitrite contributed to the cell injury. Finally, EFV increased the NADH/NAD(+) ratio, inhibited Sirt3 activity, and led to hyperacetylated lysine residues, including those in CypD. However, hepatocytes isolated from Sirt3-null mice were protected against 40µM EFV as compared to their wild-type controls. In conclusion, these data are compatible with the concept that chemical inhibition of complex I activates multiple pathways leading to cell injury; among these, peroxynitrite formation may be the most critical.

Targeting mitochondria with methylene blue protects mice against acetaminophen-induced liver injury

Acetaminophen (APAP) overdose is a frequent cause of drug-induced liver injury and the most frequent cause of acute liver failure in the Western world. Previous studies with mouse models have revealed that impairment of mitochondrial respiration is an early event in the pathogenesis, but the exact mechanisms have remained unclear, and therapeutic approaches to specifically target mitochondria have been insufficiently explored. Here, we found that the reactive oxidative metabolite of APAP, N-acetyl-p-benzoquinoneimine (NAPQI), caused the selective inhibition of mitochondrial complex II activity by >90% in both mouse hepatic mitochondria and yeast-derived complexes reconstituted into nanoscale model membranes, as well as the decrease of succinate-driven adenosine triphosphate (ATP) biosynthesis rates. Based on these findings, we hypothesized that methylene blue (MB), a mitochondria-permeant redox-active compound that can act as an alternative electron carrier, protects against APAP-induced hepatocyte injury. We found that MB (<3 µM) readily accepted electrons from NAPQI-altered, succinate-energized complex II and transferred them to cytochrome c, restoring ATP biosynthesis rates. In cultured mouse hepatocytes, MB prevented the mitochondrial permeability transition and loss of intracellular ATP without interfering with APAP bioactivation. In male C57BL/6J mice treated with APAP (450 mg/kg, intraperitoneally [IP]), MB (10 mg/kg, IP, administered 90 minutes post-APAP) protected against hepatotoxicity, whereas mice treated with APAP alone developed massive centrilobular necrosis and increased serum alanine aminotransferase activity. APAP treatment inhibited complex II activity ex vivo, but did not alter the protein expression levels of subunits SdhA or SdhC after 4 hours.

CONCLUSION

MB can effectively protect mice against APAP-induced liver injury by bypassing the NAPQI-altered mitochondrial complex II, thus alleviating the cellular energy crisis. Because MB is a clinically used drug, its potential application after APAP overdose in patients should be further explored.

A systems biology approach utilizing a mouse diversity panel identifies genetic differences influencing isoniazid-induced microvesicular steatosis

Isoniazid (INH), the mainstay therapeutic for tuberculosis infection, has been associated with rare but serious hepatotoxicity in the clinic. However, the mechanisms underlying inter-individual variability in the response to this drug have remained elusive. A genetically diverse mouse population model in combination with a systems biology approach was utilized to identify transcriptional changes, INH-responsive metabolites, and gene variants that contribute to the liver response in genetically sensitive individuals. Sensitive mouse strains developed severe microvesicular steatosis compared with corresponding vehicle control mice following 3 days of oral treatment with INH. Genes involved in mitochondrial dysfunction were enriched among liver transcripts altered with INH treatment. Those associated with INH treatment and susceptibility to INH-induced steatosis in the liver included apolipoprotein A-IV, lysosomal-associated membrane protein 1, and choline phosphotransferase 1. These alterations were accompanied by metabolomic changes including reduced levels of glutathione and the choline metabolites betaine and phosphocholine, suggesting that oxidative stress and reduced lipid export may additionally contribute to INH-induced steatosis. Finally, genome-wide association mapping revealed that polymorphisms in perilipin 2 were linked to increased triglyceride levels following INH treatment, implicating a role for inter-individual differences in lipid packaging in the susceptibility to INH-induced steatosis. Taken together, our data suggest that INH-induced steatosis is caused by not one, but multiple events involving lipid retention in the livers of genetically sensitive individuals. This work also highlights the value of using a mouse diversity panel to investigate drug-induced responses across a diverse population.

Mechanisms of isoniazid-induced idiosyncratic liver injury: emerging role of mitochondrial stress

Idiosyncratic drug-induced liver injury (DILI) is a significant adverse effect of antitubercular therapy with isoniazid (INH). Although the drug has been used for many decades, the underlying mode of action (both patient-specific and drug-specific mechanisms) leading to DILI are poorly understood. Among the patient-specific determinants of susceptibility to INH-associated DILI, the importance of HLA genetic variants has been increasingly recognized, whereas the role of polymorphisms of drug-metabolizing enzymes (NAT2 and CYP2E1) has become less important and remains controversial. However, these polymorphisms are merely correlative, and other molecular determinants of susceptibility have remained largely unknown. Regarding the drug-specific mechanisms underlying INH-induced liver injury, novel concepts have been emerging. Among these are covalent protein adduct formation via novel reactive intermediates, leading to hapten formation and a potential immune response, and interference with endogenous metabolism. Furthermore, INH and/or INH metabolites (e.g. hydrazine) can cause mitochondrial injury, which can lead to mitochondrial oxidant stress and impairment of energy homeostasis. Recent studies have revealed that underlying impairment of complex I function can trigger massive hepatocellular injury induced by otherwise nontoxic concentrations of INH superimposed on these mitochondrial deficiencies. This review discusses these emerging new paradigms of INH-induced DILI and highlights recent insights into the mechanisms, as well as points to the existing large gaps in our understanding of the pathogenesis.

Bypassing the compromised mitochondrial electron transport with methylene blue alleviates efavirenz/isoniazid-induced oxidant stress and mitochondria-mediated cell death in mouse hepatocytes

Efavirenz (EFV) is an anti-retroviral drug frequently combined with isoniazid (INH) to treat HIV-1/tuberculosis co-infected patients. Both drugs have been associated with idiosyncratic liver injury (DILI), but combined anti-retroviral and anti-tubercular therapy can increase the risk for DILI as compared to either drug class alone. Because both EFV and INH have been implicated in targeting mitochondria, we aimed at exploring whether the two drugs might cause synergistic effects on the electron transport chain. We found that EFV inhibited complex I activity in isolated mouse liver mitochondria (IC50 ˜30 μM), whereas hydrazine, a major metabolite of INH generated by acylamidase-mediated hydrolytic cleavage, inhibited complex II activity (IC50 ˜30 μM). Neither INH alone (≤1000 μM) nor EFV alone (≤30 μM) was able to induce cell injury in cultured mouse hepatocytes. However, combined EFV/INH exposure resulted in increased superoxide formation and peroxynitrite stress, leading to the opening of the cyclosporine A-insensitive mode of the mitochondrial permeability transition (mPT), and necrotic cell death. The peroxynitrite scavengers, CBA or Fe-TMPyP, protected against mPT induction and alleviated cell injury. The acylamidase inhibitor bis-p-nitrophenyl phosphate prevented cell injury, suggesting that hydrazine greatly contributed to the toxicity. Methylene blue, a redox-active alternative electron acceptor/donor that bypasses complex I/II, effectively protected against EFV/INH-induced toxicity. These data demonstrate that, in murine hepatocytes, the mitochondrial electron transport chain is a critical target of combined EFV/INH exposure, and that this drug combination can lead to peroxynitrite stress-induced mPT and hepatocellular necrosis. These results are compatible with the concept that underlying silent mitochondrial dysfunction may be a key susceptibility factor contributing to idiosyncratic drug-induced liver injury.

Role of CYP3A in isoniazid metabolism in vivo

Isoniazid (INH), a first-line drug for tuberculosis control, frequently causes liver injury. Multiple previous reports suggest that CYP3A is involved in INH metabolism, bioactivation and hepatotoxicity, although direct evidence is unavailable. In the current study, wild-type and Cyp3a-null mice were used to determine the potential role of Cyp3a in INH metabolism in vivo. Compared to wild-type mice, there were no significant differences in the pharmacokinetic profiles of INH or acetyl-isoniazid in Cyp3a-null mice after an oral administration of 50 mg/kg INH. With the same treatment, distribution of INH and its major metabolites was similar in the liver of wild-type and Cyp3a-null mice. A reactive metabolite of INH was trapped by N-α-acetyl-L-lysine in mouse liver microsomes, but Cyp3a does not contribute to this bioactivation pathway. In addition, no liver injury was observed in wild-type or Cyp3a-null mice treated with 60 or 120 mg/kg INH. In summary, Cyp3a has no effect on systemic pharmacokinetics of INH in mice. Further studies are needed to determine whether and how exactly CYP3A is involved in INH bioactivation and hepatotoxicity.